Prolific novelist and “ER” creator Michael Crichton has passed away. He was 66.

Perhaps best known for being the author of Jurassic Park and its sequel The Lost World, which were turned into a hugely successful movie franchise, his numerous books have sold over 150 million copies worldwide.

In what his family calls an unexpected death, it was revealed that he was waging a private battle against cancer.

“While the world knew him as a great storyteller that challenged our preconceived notions about the world around us — and entertained us all while doing so — his wife Sherri, daughter Taylor, family and friends knew Michael Crichton as a devoted husband, loving father and generous friend who inspired each of us to strive to see the wonders of our world through new eyes,” his family tells ET. “He did this with a wry sense of humor that those who were privileged to know him personally will never forget.”